Nearly 300 species of fish, mussels and other sea critters hitchhiked across the Pacific Ocean. They traveled on debris from the 2011 Japanese tsunami and washed ashore alive in the United States. That's what researchers reported Thursday.

It is the largest and longest marine migration ever documented, according to outside experts and the researchers. The scientists and colleagues combed the beaches of Washington, Oregon, California and British Columbia. They also combed the beaches of Alaska and Hawaii. They tracked the species to their Japanese origins. Their arrival could be a problem if the critters take root because they could push out native species. That's what the study authors said in Thursday's journal Science.

"It's a bit of what we call ecological roulette," said lead author James Carlton. He's a marine sciences professor at Williams College in Williamstown, Massachusetts.

It will be years before scientists know if the 289 Japanese species thrive in their new home and crowd out natives. The researchers roughly estimated that a million creatures traveled 4,800 miles (7,725 kilometers) across the Pacific Ocean.

Invasive species are a major problem worldwide. It’s when plants and animals thrive in areas where they don't naturally live. Marine invasions in the past have hurt native farmed shellfish. They also eroded the local ecosystem, caused economic losses and spread disease-carrying species.

A magnitude 9 earthquake off the coast of Japan triggered a tsunami on March 11, 2011, sweeping boats, docks, buoys and other man-made materials into the Pacific. The debris drifted east with an armada of living creatures. Some gave birth to new generations while at sea.

"The diversity was somewhat jaw-dropping," Carlton said. "Mollusks, sea anemones, corals, crabs, just a wide variety of species, really a cross-section of Japanese fauna."

The researchers collected and analyzed the debris that reached the West Coast and Hawaii over the last five years, with new pieces arriving Wednesday in Washington. The debris flowed across the North Pacific current, as other objects do from time to time, before it moved north with the Alaska current or south with the California current. Most hit Oregon and Washington.

Last year, a small boat from Japan reached Oregon with 20 good-sized fish inside, a kind of yellowtail jack native to the western Pacific, Carlton said. Some of the fish are still alive in an Oregon aquarium. Earlier, an entire fishing ship - the Sai sho-Maru - arrived intact with five of the same 6-inch fish swimming around inside.

Co-author Gregory Ruiz, a Smithsonian marine ecologist, is especially interested in a Japanese parasite in the gills of mussels. Elsewhere in the world, these parasites have taken root and hurt oyster and mussel harvests and they hadn't been seen before on the West Coast.

The researchers note another huge factor in this flotilla: plastics.

Decades ago, most of the debris would have been wood and that would have degraded over the long ocean trip, but now most of the debris - buoys, boats, crates and pallets - are made of plastic and that survives, Carlton said. And so the hitchhikers survive, too.

"It was the plastic debris that allowed new species to survive far longer than we ever thought they would," Carlton said.

James Byers is a marine ecologist at the University of Georgia in Athens and wasn't part of the study. He praised the authors for their detective work and said in an email that the migration was an odd mix of a natural trigger and human aspects because of the plastics.

"The fact that communities of organisms survived out in the open ocean for long time periods (years in some cases) is amazing," he wrote.

It's really cool that these fish survived with the help of plastics. It not usual that fish not native from here survived this long. This is important because it's not just Oregon and Washington in danger it's all of us. If these new species do adapt to these waters some of our many fish species may go extinct. I really hope this problem can be solved

NatalieH-del

10/04/2017 - 04:16 p.m.

I found the article interesting because I wouldn't think plastic debris would help sea creatures to survive.

PedroM-del1

10/04/2017 - 04:28 p.m.

I think this is amazing how see creatures from Japan from around 6 years ago washed up on American shores. But it is just so horrible that our oceans are being every minute. PEOPLE should be concern and donate money to marine societies to help this fragile environment. No person in the right mind wants to see a McDonald's bottle or a "Kars for Kids" flyer in the ocean. No one. NO ONE. NO ONE I SAY!!!!!

GregoryM-del

10/04/2017 - 04:36 p.m.

300 species of fish attach to debris and float on shore to migrate. Scientists have been studying the debris for several years to find out about the migration.

AkshayB-del

10/04/2017 - 04:37 p.m.

The article is considered ''hitchhiking'' since there are dead sea critters washed up on the shore. All of the sea critters were in the pacific ocean to the debris of the tsunami of japan. But now sea critters are being saved and helped by the plastic debris allowed new species.

EthanG-del1

10/04/2017 - 05:01 p.m.

Since the Sea Creatures lached on to random debris like hitchhikers.

GabriellaJ-del

10/04/2017 - 05:06 p.m.

the animals are considered hitchhiking because they moved thousands of miles across the ocean over debris and other trash.

EvanC-del

10/04/2017 - 05:11 p.m.

I thought this was a very interesting topic and its crazy how many new animals we discover in the sea like every day. Its very fascinating. I hope to learn more about it.

RushB-del

10/04/2017 - 05:32 p.m.

It's interesting to see how an event like a tsunami can create such diveristy

AnnabelleA-del

10/04/2017 - 06:08 p.m.

This was considered "hitchhiking" because the the animals cringed onto and followed the debris and kind of rode with it from Japan to the U.S.